As used herein, cancer refers to a malignant neoplasm, and cancer and tumor are regarded as synonymous.
Lymphokine-activated killer (LAK) cells exhibiting a broad antitumor activity against natural killer (NK) cell-resistant tumors can be induced by separating mononuclear cells from the peripheral blood and culturing them in the presence of interleukin-2 (IL-2) (see, for example, Grimm et al., 1982, J. Exp. Med., 155: 1823-1841). Subsequently, IL-2 has become available in large amounts as a consequence of genetic recombination technology (see, for example, Taniguchi et al., 1983, Nature, 302: 305-310), and adoptive immunotherapy using LAK cells against tumors was clinically applied and was shown to be effective (see, for example, Rosenberg et al., 1985, New Engl. J. Med., 313: 1485-1492).
It has also become possible to culture cells in the presence of anti-CD3 monoclonal antibody (MoAb) and IL-2 to obtain a large amount of cells exhibiting LAK activity from mononuclear cells derived from small amounts of peripheral blood (see, for example, Ochoa et al., 1987, J. Immunol., 138: 2728-2733).
Peripheral T lymphocytes express a CD3 molecule together with a T cell receptor (TCR) on the cell surface and are classified into helper T (Th) cells and cytotoxic T cells (CTL) depending on whether the CD4 or CD8 molecule is expressed.
Cells having a targeted cell surface antigen can be enriched or removed through the use of magnetic beads and MoAb against molecules such as CD4 molecule or CD8 molecule expressed on the cell surface (see, for example, Japanese Patent 2,530,966).
Th cells are classified into Th1 cells, which produce cytokines such as interferon-γ (IFN-γ) and IL-2, and Th2 cells, which produce cytokines such as IL-4 and IL-10 (see, for example, Mosmann et al., 1986, J. Immunol., 136: 2348-2357). Th1 cells function as an effector of cellular immunity, while Th2 cells are responsible for regulating humoral immunity. In addition, IFN-γ produced by Th1 cells inhibits Th2 cells, while IL-4 produced by Th2 cells inhibits Th1 cells (see, for example, Maggi et al., 1992, J. Immunol., 148: 2142-2147).
During the initial phase of Th cell activation, differentiation of Th1 cells is induced by the presence of IL-12 (see, for example, Seder et al., 1993, Proc. Natl. Acad. Sci. USA, 90: 10188-10192), while Th2 cell differentiation is induced by the presence of IL-4 (see, for example, Hsieh et al., 1992, Proc. Natl. Acad. Sci. USA, 89: 6065-6069).
CTLs, on the other hand, are classified into Tc1 cells and Tc2 cells based on cytokine production patterns that are the same as for the Th1 and Th2 cells. Tc1 cells exhibit a strong cytotoxicity, while Tc2 cells are responsible for immunosuppressive function. Differentiation into Tc1 cells or Tc2 cells is regulated by the presence of IL-12 or IL-4 (see, for example, Mosmann et al., 1996, Immunology Today, 17: 138-146).
T cells bind to a target cell, such as an antigen presenting cell (APC), by recognizing an MHC molecule/peptide antigen complex through the TCR. It is reported that CTLs bind to only an MHC class I molecule/peptide antigen complex (MHC class I restriction), while Th cells can bind only to an MHC class II molecule/peptide antigen complex (MHC class II restriction).
In addition, MHC class I molecules are expressed on almost all nucleated cells, while MHC class II molecules are expressed only on a limited number of cells. As a consequence, Th cells has the ability to bind to cells that express MHC class II molecules, for example, dendritic cells, B cells, and activated T cells, but are unable to directly bind to other cells, for example, tumor cells or infected cells.
However, it has been shown that MHC class II-restricted CD4+CD8− T cells genetically engineered to bear a TCR gene originating from an MHC class I-restricted CTL can be activated by reacting with an APC pulsed with the corresponding antigen in a CD8-independent manner, suggesting that the T cells express a TCR capable of binding to the corresponding antigen. In addition, a tumor can be specifically damaged by transducing a TCR gene originating in a tumor antigen-specific CTL into peripheral blood lymphocytes that have a nonspecific antitumor activity (see, for example, Morgan et al., 2003, J. Immunol., 171: 3287-3295).
In order to induce tumor-specific T cells in vitro, cancer tissue must be surgically obtained from the patient. Also it has recently become possible to induce tumor-specific T cells using tumor peptide antigen, but this procedure can be adapted only to patients with a limited type of MHC.
Moreover, substantial time and effort is required to induce tumor-specific T cells, and a large amount of blood is required to obtain APCs used for induction. These circumstances have made it difficult to obtain tumor-specific T cells in a quantity required for cell therapy.
An object of the present invention, therefore, is to provide a novel process for preparing tumor-specific T cells, particularly Th cells or both Th1 cells and Tc1 cells.
Furthermore, MHC class I molecules are expressed in almost all nucleated cells, while MHC class II molecules are expressed only in some cells including activated cells, and as a consequence helper T cells are unable to directly bind to all cells.
Another object of the present invention, therefore, is to provide a novel process for preparing tumor-specific helper T cells, particularly TH1 cells, that can bind to MHC class I molecules.